Battery charging while under way

willronco · Posted: Thu Nov 14, 2013 10:21 am Post subject: Battery charging while under way

My fellow C-Brats, I'd like to share some GREAT news. We bought a boat! And had a DELIGHTFUL shakedown cruise last weekend, about which more in another thread.

In this thread I'm trying to puzzle through a battery charging strategy and I request your help. We have 2 batteries on board - house and start. Each has a battery switch, and they can be combined with an "emergency combine" switch.

In normal operation, I have both battery switches set to ON, and the combiner set to OFF. While underway, the engine alternator charges the start battery only.

My goal is for the engine alternator to charge both batteries while the engine is running. What is the best/safest way to do this? My ideas so far are:

* Combine the batteries by turning the battery combine switch to "combine" BEFORE starting the engine. Possible advantage: no sudden voltage change while engine is running. Possible disadvantage: lower house battery impedes engine's ability to start?

* Combine the batteries by turning the battery combine switch to "combine" AFTER starting the engine. Possible advantage: more fully charged engine battery better for engine start. Possible disadvantage: flipping switch while engine is running not good for engine/alternator/something else I am not thinking of?

In the future, I'd like to install some kind of automatic switch that will do all this automatically in a smart way. This will also minimize the risk that I forget to un-combine the batteries and accidentally drain the start battery while at anchor. My guess is that device will be something like this: http://www.bluesea.com/products/7601/m-Series__Automatic_Charging_Relay_-_12_24V_DC_65A But that is probably a winter project.

For now, I really want to minimize the risk of engine damage while also charging both of my batteries while under way. Can anyone point me in the right direction on this?

AK Angler · Posted: Thu Nov 14, 2013 11:04 am Post subject:

Combine batteries after starting to charge both. And uncombine after shutting down the motor. Otherwise, you effectively have one big single battery and lose the safety benefit of having dual batteries.

PaulNBriannaLynn · Posted: Thu Nov 14, 2013 11:13 am Post subject:

I've always been told not to turn the switch while the battery is running. I think you are correct that it will send a surge through your system and possibly damage the motor electronics, or on board electronics. I cant remember which one. I have never tried it so I don't have any experience! thankfully Smile

What we do is turn the switch so we are running both batteries most of the time while we are cruising or fishing. When we are ready to anchor/dock for the night, I switch to the house battery only. Switch it back to both batteries in the morning before we start up the motors.

jerry97230 · Posted: Thu Nov 14, 2013 11:24 am Post subject:

The automatic combiner switches work very well. You do not haave to do anything or worry about forgetting to uncombine.
I have one on my boat and love it.
Jerry C Nile

AK Angler · Posted: Thu Nov 14, 2013 12:04 pm Post subject:

thataway · Posted: Thu Nov 14, 2013 1:22 pm Post subject:

Although many combine switch or the 1 2 on off switches have a make before break (field disconnect does not work with our outboards), there are some which do not. There are also older switches which do not.

The simple way is the combiner. This allows good charging of both batteries--not something to worry about (and forget), Your concerns are valid. The other concern is that it is better for electronics to not be subjected to low voltage or voltage spikes during startup. Many outboards do not have the modern regulators which we have in car alternators.

The combiners are not expensive in comparison, and can be hooked up in a very short time.

Bluechablis · Posted: Thu Nov 14, 2013 6:22 pm Post subject:

Bob, I noticed when you were getting "Thisaway" ship shape you installed a BEP VSR to you battery switch

I want to do the same for Far C'r but I am unsure of how it is wired into the switch. Does the BEP come with a wiring diagram? Is it in series with just one battery?

Hoping you can shed some light on the subject and it might help willronco as well

Chester · Posted: Thu Nov 14, 2013 9:07 pm Post subject:

Another vote for the ACR type relay.

thataway · Posted: Thu Nov 14, 2013 11:31 pm Post subject:

Basically the VSR is wired between the two input terminals of the Start and House battery. The BEP diagram often uses their on/off switch rather than the 1,2 all off switch. The Motor lead goes to the terminal in from the start battery, and "load" lead goes to the house battery battery terminal on the Perko switch.

The diagram which comes with the BEP unit is at:
http://www.bepmarine.com/media/product/pro4c27c846d96d1.pdf

willronco · Posted: Fri Nov 15, 2013 12:17 am Post subject:

Thank you very much for all the feedback, folks!

My battery combining switch is a fairly new Blue Sea systems switch, so I will not worry too much about using that switch while underway in the short term.

In addition, I will make sure to get my hands on an ACR type relay as soon as possible to minimize the risk of my own forgetfulness.

Bluechablis · Posted: Fri Nov 15, 2013 9:13 am Post subject:

Thank you Bob for digging that up. That also led me to the fact that they have a new digital VSR available that might be worth looking at

http://www.bepmarine.com/webpage-112/new-product-release-digital-voltage-sensing-relay-dvsr

Bill K · Posted: Fri Nov 15, 2013 5:58 pm Post subject:

One thing I didn't see anybody mention, do NOT turn the battery switch through or too the OFF position while the motor is running.

Bill Kelleher

tpbrady · Posted: Mon Nov 18, 2013 1:29 pm Post subject:

I vote for the ACR setup. The only thing I do recommend with the ACR is put it in a place where you can see the LED. That let's you know it is working at a glance unless you have a voltage readout on your chart plotter or other engine instrument. On my current boat with a Blue Sea ACR, I didn't rewire anything to install it. I simply ran a heavy gauge cable from the positive side of the start bank and the house bank to each terminal on the ACR and connected the ground lead. When the voltage on either bank reaches 13.6 VDC the ACR then combines the banks. This works pretty well both underway and when tied to shore power. The 110VAC battery charger is tied to the house bank and the alternator is connected to the start bank. If the ACR ever fails (I have had that happen once with a BEP setup), you can combine the banks with the battery switch and share the charge until you get the ACR repaired.

Tom